Each cylinder of an internal combustion engine is equipped with one or more gas exchange valves (e.g., intake and exhaust valves) that are cyclically opened during normal engine operation. In a conventional engine, the valves are opened by way of a camshaft/rocker arm configuration, which may additionally include a push rod. The camshaft includes one or more lobes arranged at particular angles corresponding to desired lift timings and amounts of the associated valves. The cam lobes are connected to stem ends of the associated valves by way of the push rod, rocker arm and associated linkage components. As the camshaft rotates, the cam lobes or push rods engage a first pivoting end of the rocker arm, thereby forcing a reciprocal movement of a second pivoting end of the rocker arm. This pivoting motion of the rocker arm translates to lifting and releasing or opening and closing of the associated valves. When a cylinder is equipped with more than one of the same type of gas exchange valves (e.g., more than one intake valve and/or more than one exhaust valve), all valves of the same type are typically opened at about the same time. And in order to reduce the number of camshafts, cam lobes, push rods and/or rocker arms required to open the multiple valves, a valve bridge is often used to interconnect the same type of valves with a common rocker arm.
A valve bridge generally includes a valve bridge body having a central portion and two lateral extensions. Each of the lateral extensions of the valve bridge includes a bore to receive valve stem ends. The rocker arm engages a center portion of the valve bridge between the lateral extensions. With this configuration, a single pivoting motion imparted to the center of the valve bridge by the rocker arm results in lifting of the paired valves by about the same amount and at about the same timing. A lash adjuster may be included between a cam follower and a push rod, between a push rod and a rocker arm, or in the valve bridge itself. Lash adjusters function to remove clearance that exists between the valves and corresponding seats (and/or between other valve train components) when the valve is released by the rocker arm. The lash adjuster helps to ensure sealing of the cylinder during the ensuing combustion process.
An exemplary valve bridge is disclosed in U.S. Pat. No. 9,309,788 that issued to Nair et al. on Apr. 12, 2016 (“the '788 patent”). Specifically, the '788 patent discloses a T-shaped valve bridge having a center portion and lateral extensions located at opposing sides of the center portion. A bridge cavity is formed within the center portion to receive a lash adjuster, and bores are formed within the lateral extensions to receive stem ends of associated engine valves. The lash adjuster includes a plunger, an adjuster sleeve and a check valve assembled within the bridge cavity. Additionally, the '788 valve bridge includes replaceable sleeve inserts received in the bores of the lateral extensions, the sleeve inserts configured to provide lubricating oil from a central opening therein. As such, the sleeve inserts receive valve stems and protect the valve bridge from potential damage and wear imparted thereon through friction and movement between the valve bridge and the valve stems.
Although the valve bridge of the '788 patent may be suitable for many applications, it may still be less than optimal. Specifically, for valve train components to function properly and to reduce the wear thereon, sufficient oil lubrication of the parts during engine operation is required. This is true for engines having cylinders disposed in an “in-line” configuration, as well as for engines having cylinders disposed in a “V” configuration. However, where cylinders are inclined in the V configuration, the inboard side of the valve bridge and valves are at a higher elevation than the same components on the outboard side. As such, any non-pressurized flow of oil within or on a valve bridge of a V-engine assembly requires fluid flow against gravity. Valve bridges without centrally located lash adjusters may include passages within the valve bridge body from a center portion of the valve bridge to inboard and outboard sides of the valve bridge. In such valve bridges, pressurized oil from the rocker arm may be easily transported against gravity to the inboard side of the valve bridge, thereby providing lubrication to the inboard, stem-receiving bore of the valve bridge and ultimately to the valve stem and rotator.
This pressurized oil transportation through the valve bridge is not necessarily present in valve bridges having centrally located lash adjusters, like that of the '788 patent. While the '788 valve bridge may be employed in any internal combustion engine, including in-line or V-engines, such valve bridges employed in V-engines may receive less lubricating oil on the inboard side of the valve bridge, thereby rendering them more vulnerable to wear and damage imparted through frictional contact with the valve stem. Specifically, any oil splashed onto the valve bridge or oil leaked from the valve side of the rocker arm, valve bridges and lash adjusters automatically travels under gravity in an outboard direction and needs to travel against gravity to reach inboard valve stems and valve rotators. Without such lubrication and protection, the valve bridge may wear significantly faster and need to be replaced after a shorter period of operation, thereby increasing the overall operating expenses of the engine. Accordingly, it would be beneficial to provide a valve bridge having a centrally located lash adjuster that also allows for gravitational flow of oil to the inboard side of the valve bridge and valves, as well as to the outboard components, even when inclined for V-engine configurations. Such a valve bridge may allow for oil splashed onto the valve bridge, as well as oil leaked from the lash adjuster, to be transported to both the inboard and outboard bores of the valve bridge, valve stems received therein and valve rotators associated therewith. In addition, oil distribution to both inboard and outboard valves may be further improved by providing sleeve inserts within valve bridge bores that enable broader distribution of oil within the bore.